There is considerable commercial interest in insecticidal compositions which exhibit insecticidal activity against target insects after the composition has been ingested by the target insect, especially ingestable biological insecticides. Microorganisms such as viruses and bacteria and certain products made by or within bacteria are examples of ingestible biological insecticides currently used to combat insect pests. The most widely used ingestible biological insecticide is Bacillus thuringiensis, of which many varieties are known, and products made by or within this bacterial species.
Ingestible biological insecticides have several advantages over conventional chemical insecticides such as being relatively nontoxic and nonpathogenic to nontarget organisms such as humans.
Despite the advantages of ingestible biological insecticides, they also have several disadvantages which limit their effectiveness. Among these disadvantages are low stability in the presence of decomposing organic matter and low site persistence. For example, typical commercial products employed to control mosquito larvae containing Bacillus Thuringiensis var. israelensis and the high density insecticidal crystalline protein produced by this organism are not always effective when used in an aqueous environment to kill and control mosquito larvae because these compositions tend to have high bulk density and often sink in the water to depths below the mosquito larvae feeding zone. In addition, many biological insecticides, for example, Bacillus thuringiensis, suffer lowered site persistence due to their instability, which is a result of chemical and/or physical degradation, when exposed to various environmental factors such as ultraviolet light and the like.
In order to increase the site persistence and/or stability of biological insecticides, these insecticides have been adsorbed onto latex beads (see Sehnell, D. J., Science ((1984) 223:1191) or encapsulated with lactones (see European Patent Application 145,087) or polyethylene (see Margalit, J. et al., Appl. Microbial. Biotechnol. ((1984) 19:382-383).
While encapsulation is effective in meeting some of the above stated goals, many prior art methods of encapsulation involve the use of harsh treatment procedures such as the use of organic solvents and/or heat. Biological insecticides in general are sensitive to such harsh treatments and can lose substantial activity when these encapsulation procedures are employed.
It would be desirable to have a biological insecticidal composition containing a biological ingestible insecticide that has increased stability and site persistence. It would also be desirable to have a process for preparing such insecticidal composition which avoids the use of the aforementioned harsh encapsulation procedures.
The present invention relates to insecticidal compositions of increased persistence and stability and a process for preparation thereof which involves a mild process of entrapment or encapsulation. The process of the present invention can also be applied directly to an aqueous suspension, such as to a fermentation broth or concentrate. The present invention also concerns a method of using the insecticidal compositions described herein for the control of target insects.